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Question 607 of 1,616

Security →mediumMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the IAM role's trust policy does not allow Cognito to assume it. Even when the authenticated role’s permissions policy correctly grants DynamoDB actions, Cognito must first assume that role via AWS Security Token Service using `AssumeRoleWithWebIdentity`. Without a trust policy that includes `cognito-identity.amazonaws.com` as a trusted service principal, Cognito cannot obtain temporary credentials for the user, causing all DynamoDB operations to fail. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding that an IAM role requires two policies: a permissions policy (what the role can do) and a trust policy (who can assume the role). A common trap is focusing only on the permissions policy while overlooking the trust relationship. Remember the memory tip: "Trust first, permissions second"—Cognito must be trusted before it can use any permissions.

DVA-C02 Security Practice Question

This DVA-C02 practice question tests your understanding of security. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

A developer is building a mobile application that uses Amazon Cognito for user authentication. After a user signs in, the application needs to access an Amazon DynamoDB table. The developer has set up an identity pool with an authenticated role. The IAM role attached to the authenticated identity has a policy allowing the required DynamoDB actions. However, users report that they cannot perform DynamoDB operations. What is the MOST likely cause of this issue?

Clue words in this question

Noticing these words before you look at the options changes how you read each choice.

Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

Question 1mediummultiple choice

Full question →

A
The identity pool is not configured to use the authenticated role.
Why wrong: If the identity pool were not configured, the app would likely fail to obtain any credentials entirely, but the question states the developer set up the identity pool with an authenticated role, so this is not the most likely cause.
B
The app is not passing the correct identity ID.
Why wrong: The identity ID is assigned by Cognito; the AWS SDK automatically handles this. Passing an incorrect ID would cause authentication failures, but the scenario describes users signed in and still unable to perform operations.
C
The IAM role's trust policy does not allow Cognito to assume it.
The trust policy of the IAM role must grant the Cognito Identity service principal the sts:AssumeRole permission. Without it, Cognito cannot issue credentials, resulting in denied actions.
D
The DynamoDB table is encrypted with a different KMS key.
Why wrong: If encryption with a customer-managed KMS key is used, the role would also need kms:Decrypt permissions, but the most likely initial cause is the trust policy issue.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

The IAM role's trust policy does not allow Cognito to assume it.

The most likely cause is that the IAM role's trust policy does not include a statement allowing Amazon Cognito (specifically the `cognito-identity.amazonaws.com` service principal) to assume the role. Even if the identity pool is configured to use the authenticated role and the role's permissions policy grants DynamoDB actions, Cognito must be able to assume the role via AWS Security Token Service (STS) `AssumeRoleWithWebIdentity`. Without the correct trust relationship, Cognito cannot obtain temporary credentials for the user, so all DynamoDB operations fail.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
The identity pool is not configured to use the authenticated role.
Why it's wrong here
If the identity pool were not configured, the app would likely fail to obtain any credentials entirely, but the question states the developer set up the identity pool with an authenticated role, so this is not the most likely cause.
✗
The app is not passing the correct identity ID.
Why it's wrong here
The identity ID is assigned by Cognito; the AWS SDK automatically handles this. Passing an incorrect ID would cause authentication failures, but the scenario describes users signed in and still unable to perform operations.
✓
The IAM role's trust policy does not allow Cognito to assume it.
Why this is correct
The trust policy of the IAM role must grant the Cognito Identity service principal the sts:AssumeRole permission. Without it, Cognito cannot issue credentials, resulting in denied actions.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The DynamoDB table is encrypted with a different KMS key.
Why it's wrong here
If encryption with a customer-managed KMS key is used, the role would also need kms:Decrypt permissions, but the most likely initial cause is the trust policy issue.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates often focus on the permissions policy (allowing DynamoDB actions) and overlook the trust policy, which is a separate and critical requirement for Cognito to assume the role and generate credentials.

Trap categories for this question

Scenario analysis trap
The identity ID is assigned by Cognito; the AWS SDK automatically handles this. Passing an incorrect ID would cause authentication failures, but the scenario describes users signed in and still unable to perform operations.

Detailed technical explanation

How to think about this question

Under the hood, Cognito Identity uses the `AssumeRoleWithWebIdentity` API to exchange the user's JWT token (from the user pool) for temporary AWS credentials. The trust policy on the authenticated IAM role must explicitly grant `sts:AssumeRoleWithWebIdentity` to the `cognito-identity.amazonaws.com` principal with a condition that checks the `cognito-identity.amazonaws.com:aud` claim matches the identity pool ID. A common real-world scenario is when a developer copies an IAM role from another account and forgets to update the trust policy, leading to silent failures where the identity pool appears configured but no credentials are issued.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this DVA-C02 question test?

Security — This question tests Security — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The IAM role's trust policy does not allow Cognito to assume it. — The most likely cause is that the IAM role's trust policy does not include a statement allowing Amazon Cognito (specifically the `cognito-identity.amazonaws.com` service principal) to assume the role. Even if the identity pool is configured to use the authenticated role and the role's permissions policy grants DynamoDB actions, Cognito must be able to assume the role via AWS Security Token Service (STS) `AssumeRoleWithWebIdentity`. Without the correct trust relationship, Cognito cannot obtain temporary credentials for the user, so all DynamoDB operations fail.

What should I do if I get this DVA-C02 question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

Are there clue words in this question I should notice?

Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.